CSS grid with top bar, sidebar, and repeating content

I'm having a really hard time creating the following layout using the CSS grid feature, and I'm not sure if it's even possible:

I could potentially put the top and right bars outside the grid in a table, but since the columns in the repeating part of the grid are a fixed width, I haven't found a way not to leave a space between them and the sidebar without letting them stretch.

I tried a lot of different things and none of them worked. I would think a solution would look something like that:

.my_grid {
    display: grid;
    justify-content: center;
    grid-template-columns: repeat(auto-fit, 300px);
}

.grid_top_bar {
    grid-row-start: 1;
    grid-row-end: 1;
    grid-column-start: 1;
    grid-column-end: -1;
}

.grid_right_side_bar {
    grid-row-start: 2;
    grid-row-end: -1;
    grid-column-start: -1;
    grid-column-end: -1;
}

.grid_item {
}

<div class="my_grid">
    <div class="grid_top_bar">...</div>
    <div class="grid_right_side_bar">...</div>
    
    <!-- repeating items -->
    <div class="grid_item">...</div>
    <div class="grid_item">...</div>
    <div class="grid_item">...</div>
    ...
</div>

... but of course that doesn't work. Any idea if/how this can be done?

Solution

for a variable number of column, to avoid empty gaps and with a responsive behavior, you may use

width:max-content ,
a subgrid while using specific tags for
a coherent markup (header,aside,main) instead of neutral div.

aside width:max-content on the parent, you have to set a min-width to main via calc() to avoid the empty gap and allow row wrapping according to the window's width instead a single column :

.grid {
  display: grid;
  grid-gap: 0.5em;
}

#myGrid {
  grid-template-columns: 1fr 300px;
  grid-template-rows: auto 1fr;
  grid-auto-flow: dense;
  width: max-content;
  margin: auto;
}

main {
  grid-template-columns: repeat(auto-fit, 300px);
  min-width: calc( (100vw - 400px) / 1.35);  /* make it smaller than window's removing average 400px fom aside and gaps to start width then divide (1.x) or multiplicate (0.x) to adjust */
}

header {
  grid-column: 1/3;
}

aside {
  grid-column: 2;
}

.grid> :not(.grid) {
  border: solid rgb(0, 112, 202);
  padding: 0.5em;
  background: linear-gradient(40deg, rgb(9, 164, 233), transparent, rgb(9, 164, 233), rgb(9, 164, 233), transparent), linear-gradient(-40deg, rgb(9, 164, 233), transparent, rgb(9, 164, 233), rgb(9, 164, 233), transparent) rgb(144, 215, 245);
  background-size: 8px 15px, 6px 12px
}

<div class="grid" id="myGrid">
  <header>Play me in full page mode and resize window's width to check on my behavior</header>
  <aside>...</aside>
  <main class="grid">
    <!-- repeating items -->
    <div class="grid_item">...</div>
    <div class="grid_item">...</div>
    <div class="grid_item">...</div>
    <div class="grid_item">...</div>
    <div class="grid_item">...</div>
    <div class="grid_item">...</div>
    <div class="grid_item">...</div>
    <div class="grid_item">...</div>
    <div class="grid_item">...</div>
    <div class="grid_item">...</div>
    <div class="grid_item">...</div>
    <div class="grid_item">...</div>
  </main>

</div>

codepen to play with