on focus input button and login button colliding in html

i have a login form, whose code is lie below:

.samaraveera {
  box-sizing: border-box;
  padding-right: 22%;
  padding-bottom: 3%;
  padding-top: 3%;
  display: block;
  margin: 4%;
  padding-left: 17%;

}
.samaraveera:focus + .errspan {display: none;}

.container-login100-form-btn {
  width: 97%;
  margin-top: 2%;
  margin-left: 1%;
  display: -webkit-box;
  display: -webkit-flex;
  display: -moz-box;
  display: -ms-flexbox;
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
}

.login100-form-btn {
  display: -webkit-box;
  display: -webkit-flex;
  display: -moz-box;
  display: -ms-flexbox;
  display: flex;
  justify-content: center;
  align-items: center;
  padding: 0 20px;
  width: 100%;
  height: 35px;
  border-radius: 3px;
  background: #f2136e;

  font-family: Montserrat-Bold;
  font-size: 12px;
  color: #fff;
  line-height: 1.2;
  text-transform: uppercase;
  letter-spacing: 1px;

  -webkit-transition: all 0.4s;
  -o-transition: all 0.4s;
  -moz-transition: all 0.4s;
  transition: all 0.4s;
}

.login100-form-btn:hover {
  background: #0cc3eb;
}

<input class="samaraveera" type="text" placeholder="Phone Number">
<span class="fa fa-phone errspan"></span>
</div>
<div class="sellois">

  <input class="samaraveera" placeholder="Password" type="password" name="pass">
  <span class="fa fa-lock errspan"></span>
</div>

<div id="paaths" class="container-login100-form-btn">
  <button class="login100-form-btn">
							Sign in
						</button>
</div>

when the input box is focused for entering values, its moving. And the password input box is colliding with login button like below image:

I have one more issue with this input box, when the page loads it loads with the correct width, when I enter some value or focus the input box then the width of the box increases a bit. can anyone please tell me what could be the problem here, thanks in advance

Solution

First try to use container aligned in center of screen I think. After that your inputs needs to be in certain width to block them from moving.

.container {
  position: fixed;
  width: 300px;
  height: 300px;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  padding: 20px;
}

.form-title {
  width: 300px;
  height: auto;
  padding: 10px;
}

.form-item {
  width: 100%;
  height: 30px;
  border: 1px solid #929292;
  border-radius: 5px;
  display: flex;
  flex-direction: row;
  align-items: center;
  transition: all .3s;
  margin-bottom: 10px;
}

.form-item:focus-within {
  border: 1px solid #ffffff;
}

.icon {
  width: 10%;
  height: 30px;
  background-color: #f2136e;
}

.form-item [type=text], [type=password] {
  width: 90%;
  background-color: transparent;
  border: none;
}

.form-links {
  text-align: center;
  margin-bottom: 20px;
}

.form-links a {
  text-align: center;
  text-decoration: none;
  color: #f2136e;
  font-size: 14px;
}

.form-btn {
  width: 100%;
  height: 40px;
}

.form-btn [type=button]{
  width: 100%;
  height: 40px;
  background-color: #f2136e;
  border: none;
  color: #fff;
  border-radius: 5px;
}

.form-register{
  width: 100%;
  height: 40px;
}

.form-register [type=button]{
  width: 40%;
  height: 40px;
  background-color: transparent;
  border: 2px solid #f2136e;
  color: #f2136e;
  border-radius: 5px;
}

<div class="container">
  <div class="form-title"> LOG IN </div>
  <hr/>
  <div class="form-item">
    <div class="icon"></div>
    <input type="text" name="phone-number" placeholder="Phone number">
  </div>
  <div class="form-item">
    <div class="icon"></div>
    <input type="password" name="phone-number" placeholder="Password">
  </div>
  <div class="form-btn">
    <input type="button" name="submit" value="Sign in">
  </div>
  <div class="form-links">
    <a href="#">RESET PASSWORD</a> | <a href="#">LOGIN WITH OPT</a>
  </div>
  <div class="form-register">
    <input type="button" name="register" value="SIGN UP HERE">
    <span> NEW USER? </span>
  </div>
</div>