Would like to have equal widths for my flex item buttons, but not sizing at all

Question

I am trying to size the Sure and Cancel buttons to be the same size. I placed them in a flexbox container with display: flex. Then, I put flex: 1 for .button.sure and .button.cancel, but the flex items are not responding at all.

I am working on the assumption that putting display: flex on the container and then its flex items with flex: 1, should do the trick, but I have no idea why these items aren't responding.

I thought maybe the button tags were causing an error with the flex: 1 declaration, so tried nesting the <button> in <div> and that didn't work too.

Here is what I have:

.icon {
 background-color: lavender;
  height: 42px;
  width: 42px;
  display: flex;
  justify-content: center;
  align-items: center;
  border-radius: 50%;
  font-weight: 700;
  font-size: 26px;
  color: royalblue;
}

.prompt {
  display: flex;
  flex-direction: column;
  align-items: center;
}

.buttonbox {
  display: flex;
  background: lavender;
}

.button{ 
  border-radius: 5px;
}

.button.sure {
  background: royalblue;
  color: white;
  flex: 1;
}

.button.cancel {
  background: white;
  color: royalblue;
  flex: 1;
}

<div class="prompt">  
  <div class="icon">!</div>
  <div class="buttonbox"> 
    <button class="button sure">Sure</button>
    <button class="button cancel">Cancel</button>
   </div>
</div>

Answer 1

Replace your flexbox with grid. If you set the grid-template-columns to 1fr then each child will occupy the same size. More info on CSS tricks and there's a nice video from Kevin Powell

.icon {
 background-color: lavender;
  height: 42px;
  width: 42px;
  display: flex;
  justify-content: center;
  align-items: center;
  border-radius: 50%;
  font-weight: 700;
  font-size: 26px;
  color: royalblue;
}

.prompt {
  display: flex;
  flex-direction: column;
  align-items: center;
}

.buttonbox {
  /*replaced flex with grid */
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  background: lavender;
}

.button{ 
  border-radius: 5px;
}

.button.sure {
  background: royalblue;
  color: white;
  /*flex: 1; delete this, not needed*/
}

.button.cancel {
  background: white;
  color: royalblue;
  /*flex: 1; delete this, not needed*/
}

<div class="prompt">  
  <div class="icon">!</div>
  <div class="buttonbox"> 
    <button class="button sure">Sure</button>
    <button class="button cancel">Cancel</button>
   </div>
</div>