How to make an inline-block element fill the remainder of the line?

Question

See: http://jsfiddle.net/qx32C/36/

.lineContainer {
    overflow: hidden; /* clear the float */
    border: 1px solid #000
}
.lineContainer div {
    height: 20px
} 
.left {
    width: 100px;
    float: left;
    border-right: 1px solid #000
}
.right {
    overflow: hidden;
    background: #ccc
}

<div class="lineContainer">
    <div class="left">left</div>
    <div class="right">right</div>
</div>

---

Why did I replace margin-left: 100px with overflow: hidden on .right?

A modern solution using flexbox:

.container {
    display: flex;
}
.container > div {
    border: 1px solid black;
    height: 10px;
}

.left {
   width: 100px;
}

.right {
    width: 100%;
    background-color:#ddd;
}

<div class="container">
  <div class="left"></div>
  <div class="right"></div>
</div>

http://jsfiddle.net/m5Xz2/100/

Compatible with common modern browers (IE 8+): http://jsfiddle.net/m5Xz2/3/

.lineContainer {
    display:table;
    border-collapse:collapse;
    width:100%;
}
.lineContainer div {
    display:table-cell;
    border:1px solid black;
    height:10px;
}
.left {
    width:100px;
}

 <div class="lineContainer">
    <div class="left">left</div>
    <div class="right">right</div>
</div>

You can use calc (100% - 100px) on the fluid element, along with display:inline-block for both elements.

Be aware that there should not be any space between the tags, otherwise you will have to consider that space in your calc too.

.left{
    display:inline-block;
    width:100px;
}
.right{
    display:inline-block;
    width:calc(100% - 100px);
}


<div class=“left”></div><div class=“right”></div>

Quick example: http://jsfiddle.net/dw689mt4/1/

I've used flex-grow property to achieve this goal. You'll have to set display: flex for parent container, then you need to set flex-grow: 1 for the block you want to fill remaining space, or just flex: 1 as tanius mentioned in the comments.